The present invention relates to an air sifting or settling apparatus for preparatory concentration of raw materials including, in particular, coal.
Known air sifting apparatus comprise a material feed device, a material bed support device with holes through which flows air guided by an air plenum disposed underneath the material bed support device, the inflowing air operating to loosen the material which has been fed onto the material bed support device in a manner by which the material on the material bed support device is stratified into layers of relatively lighter material on top of layers of relatively heavier material, and a usual discharge control device for controlling the separated discharge of the relatively lighter material and the relatively heavier material. An air sifting apparatus of this type is described, for example, in the publication Schubert xe2x80x9cAufbereitung fester mineralischer Rohstoffexe2x80x9d, Band II VEB Deutscher Verlag fuer Grundstoffindustrie, Leipzig, Pages 89 and 90.
In considering the known air sifting apparatus, it has typically been viewed as a disadvantage that, in comparison with wet sifting machines having the same operating principle, only a small separation distinction exists between the heavier material and the lighter material. In this regard, a satisfactory sorting result can be expected only if the density difference between the components of the material to be separated is sufficiently large and if the material is narrowly classified within a relatively narrow size rangexe2x80x94that is, if it lies within a narrowly defined kernel or grain size range. Moreover, the top surface of the material must be low in surface moisture since otherwise capillary retention forces hinder the relative movement of the kernels or grains. A further problem with such known air sifting apparatus is that the pressure drop differs relatively greatly as the material being transported on the material bed support device is subjected to the through flow of the air and pulsating movement. Thus, the area of the material feed-in end of the material bed support device, with a large layer thickness, is characterized by a greater pressure drop than the area at the outlet end of the material bed support device at which a stratification of the material bed has already been effected.
The aforementioned Schubert publication describes, as a solution to this drawback, a Soviet air sifting apparatus construction in which a packing of ceramic balls are located underneath the material bed support device, with the thickness of the packing being varied in correspondence with the anticipated resistance of the bed of the material bed support device so that the pressure drop of the ball packing and the comprehensive portion of the bed of the material bed support device can be influenced. A generally uniform pressure drop can be introduced by this approach along the length of the material bed support device.
The present invention provides an air sifting apparatus which offers a solution to the challenge of providing an air sifting apparatus in which a uniform pressure drop can be instituted without excessive effort across the surface of the material bed support device, whereby a good separation result in view of the material to be separated can be achieved.
The solution to this challenge is principally comprised of providing an air jig hutch or plenum for transmitting two air flows which are delivered to the air sifting apparatus and which flow through the bed thereof, wherein one of the air flows constantly flows through the material bed support device and the other air flow flows in a pulsing manner overlaid on the constant air flow. A base fluidization of the material to be prepared and disposed on the material bed support device is provided by the impact thereagainst of the constant air flow such that a certain loosening of the material is effected which is characterized by a reduced pressure loss due to the vertical through flow of the material bed support device by the air flow. In this manner, in view of the overlaid pulsating air flow, there is required only a significantly reduced volume of pulse air, as compared to conventional requirements, to effect periodic uplifting of the material disposed on the material bed support device so as to thereby accomplish a stratification of the material. The constant air flow can be adjusted such that material which has been disposed on the material bed support device is loosened but not yet uplifted, whereupon the pulsating air flow is adjusted to a pulse strength sufficient to lift the material upwardly and thereby effect stratification of the bed of material into relatively heavier material layers and relatively lighter material layers.
In accordance with embodiments of the air sifting apparatus of the present invention, the pressure of the pulsating air flow can be adjusted to be the same as or, alternatively, to be greater than, the pressure of the constant air flow.
It can further be provided, in accordance with the present invention, that the flow volume of the pulsating air flow can be adjusted to be smaller than the flow volume of the constant air flow.
In accordance with one variation of the air sifting apparatus of the present invention, two air flow generators are provided for the respective production of the constant air flow and the pulsating air flow, or a common air flow generator for the production of both the constant air flow and the pulsating air flow is provided, whereby the adjustment of the air flow at the air jig plenum is accomplished via a pressure regulator.
In accordance with an embodiment of the present invention, the material bed support device can be configured as a polyurethane screen deck, a plate with holes or as a wire screen, such as woven wire or profile wire in all configurations, whereby the material bed support device exhibits sufficient restriction for an even distribution of air flow yet is sufficiently open to allow a pass through capability for the passage therethrough of the constant air flow as well as for the passage therethrough of the constant air flow with the pulsating air flow overlaid thereon.
In accordance with an embodiment of the air sifting apparatus of the present invention, it is advantageous if the material feed-in device which feeds the material onto the material bed support device is configured such that there is provided a uniform volume of feed of the material to be prepared onto the material bed support device. By feeding or dosing the material onto the material bed support device in as uniform a unit volume as possible, an overfilling of the material bed support device is avoided; such overfillings would lead, in certain regions of the air sifting apparatus, to a breakdown of the fluidization effected by the constant air flow.
In accordance with an embodiment of the air sifting apparatus of the present invention, the material feed in device is configured as a star gate feeder. In view of the fact that a constant material feed in capability of the star gate feeder over a predetermined operational period of the air sifting apparatus can be ensured only if, in connection with the vanes which rotate within the fixed housing of the star gate feeder and are arranged in a star pattern to form pockets between adjacent vanes for dose feeding of the material onto the material bed support device, the wear of the vanes can be limited, the present invention proposes as well a novel configuration of the star gate feeder. In view of the fact that, in the realm of conventional star gate feeders, a star gate feeder is typically integrally formed as a single unit, it is a special feature of the present invention that the vanes are each formed of a rubber material whose hardness grade or durometer varies along the height of the vane, whereby the end of the vane which slides along the inner wall of the housing has a reduced hardness grade or durometer as compared to that of the end of the vane secured to the drive shaft. This feature advantageously ensures that, on the one hand, the radially outermost end of the vane which slides along the inner wall of the housing and forms a material receiving pocket with an adjacent vane is prevented, by virtue of its construction with the relatively lowest hardness grade or durometer of rubber material, from binding on the inner wall of the housing while, on the other hand, the other end of the vane, by virtue of its construction with the relatively highest hardness grade or durometer of rubber material, is secured in a sufficiently stable manner to the drive shaft of the star gate feeder and, additionally, cannot be easily broken when subjected to performance demands in question.
In accordance with the present invention, it is purposefully suggested that the vane comprise, over at least 5% of its total length as measured from its radially outermost end, the rubber material of the relatively lowest hardness grade or durometer and/or that the vane comprise, over at least 25% of its total length as measured from its drive shaft secured end, the rubber material of the relatively highest hardness grade or durometer. In this manner, it has been shown to be advantageous if the radially outermost end of the vane which slides along the inner wall of the housing is configured in a ball shape.
In addition to providing the important function of a good separation distinction between the components of the material subjected to the concentration process, the air sifting apparatus of the present invention also provides the important function of a good discharge control of the stratified material and, in particular, of the relatively heavier material thereof, in that the discharge of the stratified material from the material bed support device is performed in a manner which is automatic and avoids the undesired pressure drop which would otherwise be unfavorably promoted by stronger fluctuations of the relatively heavier material layer caused by too strong drawing off of the relatively heavier material from the material bed support device.
In accordance with an embodiment of the air sifting apparatus of the present invention, the discharge control device can comprise a mechanical or nuclear sensor for sensing the position of the higher density layers, whereby, in both sensor configurations, the sensors are configured with respect to the differing thickness of the relatively heavier material and the relatively lighter material. An alternative possibility is that the discharge control device can comprise an appropriate optical sensor for determining relatively higher density material from the lower density material by sensing the different colors of the relatively heavier material and the relatively lighter material.
In individual situations, in accordance with an embodiment of the air sifting apparatus of the present invention, the discharge control device for the relatively lighter material can be configured as a weir whose height is adjustably settable as a function of the strength or thickness of the relatively heavier material layer in its role as a sifting bed, whereby, in another embodiment of the air sifting apparatus of the present invention, the discharge control device is configured as a star gate feeder having an adjustable rate of rotation.